1. Technical Field
The present invention relates to an image sensor packaging structure and, more particularly, to an image sensor packaging structure having a predetermined focal length and equipped with an optical assembly which is assembled, tested, and calibrated in advance.
2. Description of Related Art
Image sensors are configured to receive light in the surrounding space and convert optical signals into electrical signals and are therefore widely used as a key component in a variety of photoelectric products. A conventional image sensor packaging structure is typically made in the following manner. An image sensor chip is disposed on a substrate and electrically connected thereto by conductive wires. Then, a light-transparent lid or a lens set is provided above the image sensor chip such that light passing through the light-transparent lid or the lens set can be captured by the image sensor chip. After packaging, the resultant image sensor packaging structure is ready for use by a system manufacturer. For example the image sensor packaging structure can be integrated into an external device, such as a printed circuit board, and applied to a digital still camera (DSC), a digital video recorder (DV), a surveillance device, a cell phone, an image sensor module for vehicles, and many other electronic products.
In order to satisfy consumers' demands of electronic products, manufacturers have spared no effort in downsizing the image sensor packaging structure and simplifying its packaging process. For instance, referring to FIG. 1 for an image sensor packaging structure disclosed by U.S. Pat. No. 6,972,497, which is entitled “Optical Semiconductor Device and Method of Manufacture” and granted on Dec. 6, 2005, a sensor chip 1 is provided with conductive wires 2 for electrically connecting the sensor chip 1 to an underlying substrate or carrier. Then, a supporting member 3 is provided above the sensor chip 1, and a dam 4 is formed around and at some distance from the sensor chip 1. Afterward, a polymer encapsulation 5, made of epoxy for example, is used to embed the conductive wires 2, before a lens holder 6 is provided on the supporting member 3.
The image sensor packaging structure of the above-cited US patent has the following drawbacks. First of all, the manufacturing method is complicated. Secondly, the supporting member 3 incurs high production costs and material costs. Thirdly, the polymer encapsulation 5 has high material costs and low productivity. Fourthly, the assembly tolerances between the sensor chip 1 and the supporting member 3 and between the supporting member 3 and the lens holder 6 are so large that it is structurally difficult to provide a predetermined focal length More specifically, the optical assembly tends not to focus on the sensitization area of the image sensor but to cause an out-of-focus phenomenon. Last but not least, since each image sensor must be tested and calibrated individually, the time and costs required for the entire manufacturing process are increased. As a result, the cycle time of the manufacturing process cannot be effectively shortened, which in turn hinders improvement in throughput per unit time.